In the application of electromagnetic technique for investigation of electrical conductivity of ground subsurface layers, it is often necessary to use an inductive sensor with very large dynamic range in terms of bandwidth and effective area. Unfortunately, requirements of large effective area and wide bandwidth are typically difficult to achieve in a practical-size single sensor. Therefore, to achieve these requirements, typically two separate sensors (typically separate coils) are used, one with a large bandwidth but small effective area, and one with large effective area but small bandwidth. The results of measurement using the two separate sensors are later combined.
The procedure using two sensors is typically to perform the measurement using two coils such that during the measuring cycle, the two coils are separated by a substantial distance so that they do not affect interfere with each other. Since in most cases it is desirable that measurements with two coils are performed at the same place, the two measurements using the two coils cannot be performed simultaneously.